The invention relates to a method for casing drilling, the method comprising: drilling rock by rotating an inner rod by a rotation device included in a rock drilling machine, and breaking rock by at least one drill bit and pulling an outer tube into a borehole during drilling; forming extension drill equipment by joining two or more inner rods one after another in the longitudinal direction and by correspondingly joining two or more outer tubes one after another in the longitudinal direction; turning the inner rod about its longitudinal axis when the inner rods are joined together or when the extension drill equipment is disassembled; turning the outer tube about its longitudinal axis when the outer tubes are joined together or when the extension drill equipment is disassembled; performing the turning needed to join the inner rods and the outer tubes non-simultaneously; performing the rotation of the inner rod and the outer tube by means of the rotation device of the rock drilling machine and an adapter device connected thereto when the extension drill equipment is being assembled or disassembled.
The invention further relates to a drilling unit comprising: a rock drilling machine including at least one rotation device for rotating at least one inner rod about its longitudinal axis; a feed mechanism for moving the rock drilling machine; and a feed beam which supports the rock drilling machine and on which the rock drilling machine is moved forward towards the rock to be drilled and backwards; and an adapter device arranged to transmit the rotation force generated by the rotation device of the rock drilling machine to the inner rod; the adapter device comprising an elongated inner piece whose first end receives the rotation force generated by the rotation device and whose second end is connectable to the inner rod; the adapter device further comprising an outer piece, which is an elongated tubular piece, which is arranged at least partly around the inner piece and whose second end is connectable to the outer tube used in casing drilling.
The invention further relates to an adapter device for transmitting rotation force from a rotation device of a rock drilling machine to at least one tool, the adapter device comprising: an elongated inner piece having a first end and a second end; the first end of the inner piece comprising first means enabling transmission of rotation force from the rotation device of the rock drilling machine to the inner piece and the second end of the inner piece comprising second joining means enabling connecting the inner piece to the inner rod; an outer piece, which is an elongated tubular piece having a first end and a second end and which is arranged at least partly around the inner piece; the second end of the outer piece comprising third joining means enabling connecting the outer piece to an outer tube used in casing drilling.
When a tunnel is excavated in broken or soft rock or in a rock having an otherwise poor quality for excavating a tunnel, the tunnel walls and ceiling may have to be supported by various anchorings, bolts and by injecting concrete or another filler into boreholes. It is also known to support the walls and ceiling of a tunnel already before starting the actual tunnel excavation. In that case, casing drilling may be employed where several boreholes are drilled next to one another according to the profile to be formed for the tunnel afterwards. In casing drilling, a casing is introduced into a borehole during drilling, where it may be left to support the poor-quality rock. In casing drilling, double equipment is used, i.e. drilling is performed by rotating a drill rod or a corresponding inner rod and by possibly rotating a casing around it or a corresponding outer tube by the drill's rotation device. The outermost end of the casing is provided with a ring bit and the outermost end of the drill rod with an inner bit. When the drilled borehole is sufficiently deep, the drill rod and the inner bit are withdrawn from the borehole. The casing can be left in the borehole, in which case it forms an element supporting the borehole. Furthermore, concrete, another soldering material and necessary supporting members may be fed into the casing.
When long boreholes are drilled, casing drilling is performed as extension drill equipment drilling. In that case, the drilling components employed in casing drilling, i.e. drill rods and casings are connected one after the other in the longitudinal direction. Both the drill rods and the casings may be provided with joining threads for connecting. When the drilling equipment is extended, it has to be possible to turn both the drill rods and the casings about their longitudinal axis so that the joining threads of successive drilling components can be connected together. Correspondingly, when the drilling equipment is disassembled, it has to be possible to turn the drilling components about their longitudinal axis to disconnect the joining threads. However, the connecting of drill rods and casings must be performed non-simultaneously, in which case it has to be possible to turn the drill rod and casing to be connected regardless of each other. Prior art drilling units employed in casing drilling are provided with a separate turning unit for turning the casing regardless of the drill rod when casings are being connected to or disconnected from each other. Such a turning unit, however, disadvantageously increases the weight of the drilling unit and causes extra costs and additional need for maintenance.